Avis
, , , , , | abbreviation = Avi | genitive = Avis | pronounce = Ā•vis | symbolism = the | dino = Olaj | dinoabbrev = Ola | dinogen = Olaj | dinopronounce = Ō•laj | mRA = | mdec= | ndec = | sdec = | wRA = | eRA = | quadrant = NQ3 | bordering = Araneus Felis Noctua Tarandus Testudo | area = 4465.763 sq. deg. (3 ) | proportion = 108.253‰ | average = 744.294 sq. deg. (2 ) | namedstars = 47 | mainstars = 12 | nakedeyestars = 331 | bfstars = 366 | ehstars = 52 | brightstars = 16 | brighteststar = (0.03 }}) | nearbystars = 22 | neareststar = (2.55 , 8.31 ) | messierobjects = 12 | fullrange = 90°N–0° | partialrange = 0°N–62°S | date = March 21 | solarzodiac = N/A | tropicalzodiac = N/A | siderealzodiac = N/A }} Avis (Latin for ) is a caelregio with midpoint located in third of the . This caelregio is around the in which all meridians cross this caelregio. Avis is composed of six s (the list is at the top of the infobox to the right). Avis covers about 108‰ of the sky with an area of 4466 square degrees, making it the third largest caelregio after Chtapodi and Noctua. Despite its name, Avis contains just one constellation named after a bird: the . Avis contains two famous s: the and the . This caelregio also contains the bright north star at the handle of the Little Dipper. Notable stars Bright stars Avis contains the current bright north Polaris located in . Polaris is an of magnitude 1.97. However, Polaris is not the brightest star in Avis. At a of 0.03, an is the Avis' brightest star and is also the fifth brightest overall, located in . At around 14000 AD due to the , Vega will be the north pole star. Besides Polaris and Vega, , located in Cygnus (a 1.25 A-type ), is also notably bright. Deneb is one of the stars that make up the , the other two are Vega (just mentioned above) and , which is located in the neighboring caelregio Tarandus. Deneb is the sky's northernmost first magnitude star. Nearby stars At a of 8.31 s (2.55 s), a is the Avis' nearest star and is also the fourth nearest star system overall, located in . Lalande 21185 had two planets that were now regarded doubtful. Another notable nearby star in Avis is in Ursa Major, which is a rare which can produce s hundreds to millions of times more powerful than the largest flares ever observed on the Sun. This star is only about 3–10% as enriched with elements heavier than helium as the Sun, making this a . Variable stars The is located in Lyra. The variability lasts 13 hours and varies between magnitudes 7.06 to 8.12. RR Lyraes are often used as s to measure galactic distances. Another variable star in Lyra is . Beta Lyrae variable is a type of which the stars have ellipsoidal shape and undergoing . Its magnitude varies from 3.25 to 4.36 over its 12.9 day period. The variable star is located in Draco. Its average period is about 3.8285 days but the brightness varies over several years depending on its stellar activity. This variability is caused by movements of s due to its rapid rotation. Unlike the Sun where the s originate from the equator, the group of starspots on BY Dra variables originate from the poles. The variable star is located in Ursa Major. Like and β Lyr types, W UMa variables is a type of eclipsing binary. W UMa variables including the prototype star are whose both component stars share a common outer layer. Its magnitude varies from 7.75 to 8.48 over the period of 8 hours. Another variable star in Ursa Major is . With , this type is the . AN UMa has the strongest known of any cataclysmic variables at 230 million or 23 . The magnitude of this star varies between 14.9 and 20.2. Extopically, AN UMa is a , that means that this red dwarf abnormally contains more than . Polaris is interestingly a . Around 1900, Polaris' luminosity varied ±8% from its average (0.15 magnitude in total) with a 3.97 day period. Today, the variability period is now 3.98 days, which is 15 minutes longer than it was around the turn of the 20th century. Researchers suggest that Polaris is 2.5 times (about 1 magnitude) brighter today than it was during the 's time in the 2nd century. Multiple stars Cygnus contains four interesting binary stars: , , Beta Lyrae, Epsilon Lyrae, and ; plus the quadruple star system . Albireo is composed of K-type and B-type stars that takes 214 years to orbit each other. 61 Cygni is an interesting star because it was the first star other than our Sun to have its distance measured in 1838 by . He measured it as 10.4 light-years, very close to the modern value of 11.4 light-years. Both stars in 61 Cygni system are K-type and take 659 years to orbit around the . 61 Cygni is speculated to have seven planets, three orbit component A and four orbit component B. Beta Lyrae in Lyra is another interesting binary star. It is a which the less massive star is undergoing mass transfer to its more massive companion. Epsilon Lyrae in Lyra is a famous 'double- . Using the , Epsilon Lyrae just appears to be composed of just two stars but a shows that each star is itself double. Mizar contains two binary stars. Located 0.5–1.5 light-years from Mizar lies another binary star system Alcor. The s show that Alcor and Mizar share a common motion through space and they are physically bound. These two star systems comprise the . The Mizar-Alcor system comprises a total of six stars and three binary stars. The Mizar-Alcor system can sometimes be referred as " ." Mizar was observed to be double by in 1650 (and probably earlier by and in the early 1600s). Polaris is in fact a containing five stars, even though it just appears as a single star to the . Double stars in Ursa Major is an optically that was formerly thought to be a . The two stars are separated by 51.7 , easily separable using the naked eye. Planetary systems As of August 8, 2011, there are 52 known s in Avis. One notable example is (P1 Avi) in Ursa Major, which contains three s. The names (planet numbers) are Clio (P14), Euterpe (P62), and Mnemosyne (P402). They have of 2.08, 3.53, and 11.48 respectively. The masses are 2.84, 0.60, and 1.76 ]] respectively. (P2 Avi) in Cygnus has a giant planet (P18) in . Althaea orbits the component 16 Cygni B. Althaea has mass 1.70 M and orbits at a distance of 1.69 AU with an of 0.69. (P5 Avi) in Ursa Major has a Niobe (P60) with the most elliptical orbit (e=0.93366) of any known exoplanets. Astronomers found that the shocking winds on can reach up to 3 as gases rush from the hot day side to the cool night side. An example of planetary system detected by is (P43 Avi) in Draco, which contains the first rocky planet detected by Kepler: (P496). Kepler-10 also contains the midplanet (P524). Another example of planetary system detected by Kepler is (P44 Avi) in Cygnus, which contains six planets: five super-Earths and one midplanet. All six orbit within 0.5 AU, making it the most compact planetary system known. All of the numerous Kepler planets are detected in this caelregio since Kepler can only be designed to find planets in the Avian constellations Cygnus, Draco, and Lyra. Notable deep sky objects Avis contains a lot of interesting deep sky objects. The ( 101, 5457) is a located in Ursa Major. The (NGC 7000, 20) is a located in Cygnus. The ( 5070 and IC 5067) is an associated with the North American Nebula in Cygnus. Also in this constellation, we find the (also known as the Cirrus Nebula or Filamentary Nebula) (NGC 6960, C34), which is a within the .Within this nebula, there is the prominent feature . In the same constellation, we find the (NGC 6888, C27), which is an , the (IC 5146, C19), which is a stellar nursery, and the (IC 1318), which is a . There is the (NGC 6946, C12) in Cygnus, where nine supernovae have been observed in this since 1900. Another galaxy in Cygnus is ( 405), which is an . Cygnus A is the most famous and is among the radio sources in the sky. In Ursa Major, there is the (M81, NGC 3031), which is a nearby active spiral galaxy located some 12 million light-years from the . This galaxy is with M82 to be mentioned and . Also in this constellation, we find the nearest (M82, NGC 3034) at 11 million light-years away, which is an . , which is a , can be seen famous in Ursa Major. In Draco, there is the ( 10214), which is a disrupted , can be seen using a . The Tadpole Galaxy has a tail of s shaped by the gravitational influence of a passing galaxy. Also in this constellation, the (M102, NGC 5866, C53) –– a , and (C3) –– a barred spiral galaxy, can be seen using a small telescope. The (NGC 6543, C6) is a also located in Draco. The (M97) is also a planetary nebula located in Ursa Major. The (CRL 2688) is a located in Cygnus. The (M57, NGC 6720) is a planetary nebula in Lyra. The (NGC 6826, C15) and the (NGC 7008) are both planetaries in Cygnus. In Cepheus, there is the . Gallery Notable meteor showers Every year around December 22, the (also called December Avids) peak in the constellation Ursa Minor. This is controversally caused by the . It can produce about 10 meteors per hour. Another meteor shower in Avis is (also called April Avids), which peak around April 22 every year in the constellation Lyra. This shower is caused by the periodic . It produces an average about 10 meteors per hour, but sometimes during the , up to 90 meteors per hour are visible. Visibility In the northern hemisphere, Avis can most prominently be visible from mid fall till mid summer. In the north temperate zone such as in the United States' Midwest, Europe, and central Asia, about half of this caelregio would be circumpolar. From north of 62°N in places like Siberia, Scandinavia, Greenland, and Alaska, all of Avis would be circumpolar as it rotates clockwise around the sky once a day and once a year at a given time. From south of 62°S like in Antarctica, Avis would never rise. Avis contains two prominent asterisms: the in Ursa Major and the in Ursa Minor. Both Dippers contain bowl of fours stars and handle of three stars. The Big Dipper is highest from late winter till early spring while the Little Dipper is highest from mid to late spring. But from north of 40°N, both Dippers can be seen rotating around the north pole and therefore both Dippers can be visible all-year round. Polaris is a useful pole star for northern observers and for because that star is where the direction of north lies since that star virtually stays at a same point of the sky annually. So all other stars including the Little Dipper appear to rotate around Polaris. Even without devices, time of the day and year can still be determined by the orientation of the Little Dipper relative to Polaris. Zodiac Since the never crosses Avis, this is not a al caelregio. Category:Articles Category:Caelregios